1. Field of the Invention
This invention relates generally to semiconductor wafer fabrication systems, and, more particularly, to methods and systems for removing particles from surfaces of semiconductor wafers during semiconductor wafer fabrication.
2. Description of the Related Art
Integrated circuits are typically formed by processing several semiconductor wafers as a group or xe2x80x9clotxe2x80x9d through a series of wafer fabrication process tools (i.e., xe2x80x9cprocess toolsxe2x80x9d). Each process tool typically performs a single wafer fabrication operation upon the semiconductor wafers. The integrated circuits formed in this manner are substantially identical to one another. Following wafer fabrication, the integrated circuits are typically subjected to functional testing, then separated. An individual integrated circuit is called a xe2x80x9cchipxe2x80x9d or a xe2x80x9cdie.xe2x80x9d Fully functional die are typically packaged and sold as individual units.
It is well known that small particles (i.e., particulates) which adhere to surfaces of semiconductor wafers during wafer fabrication cause xe2x80x9cdefects.xe2x80x9d In general, a xe2x80x9cdefectxe2x80x9d is a flaw resulting from an imperfect manufacturing process. Particulates are present in the ambient air, introduced by processing personnel, suspended in liquids and gasses used during wafer processing, and generated by processing equipment. A defect which prevents an integrated circuit containing the defect from performing its intended function is termed a xe2x80x9ccatastrophicxe2x80x9d or xe2x80x9ckillerxe2x80x9d defect. As catastrophic defects reduce yields of wafer fabrication processes, integrated circuit manufacturers go to great lengths to reduce the number of particulates which may adhere to surfaces of semiconductor wafers during wafer fabrication processes.
In general, the vulnerability of a particular integrated circuit feature to a given defect is inversely proportional to the physical dimensions of the feature. Thus as physical dimensions of integrated circuit features shrink over time, the likelihood that a given particulate will cause a xe2x80x9ccatastrophicxe2x80x9d defect increases over time. It would thus be beneficial to have a system and method for selectively removing particles from surfaces of semiconductor wafers. Employing such a system and method during a wafer fabrication process may increase a yield of the wafer fabrication process.
A method is described for removing a particle from a surface of a semiconductor wafer. In general, the method involves positioning an electrically conductive surface near the particle to be removed. An electrical charge is created on the electrically conductive surface. A charged particle beam is formed, wherein the charged particle beam includes particles having an electrical charge opposite the electrical charge of the electrically conductive surface. The charged particle beam is directed at the particle to be removed to impart an electrical charge opposite the electrical charge of the electrically conductive surface on the particle. When struck by the charged particle beam, the particle to be removed absorbs a portion of the charged particles of the charged particle beam and acquires an electrical charge opposite the electrical charge of the electrically conductive surface. A force created between the opposed electrical charges of the particle to be removed and the electrically conductive surface causes the particle to be removed to move from the surface of the semiconductor wafer and toward the electrically conductive surface.
The electrically conductive surface may be, for example, a surface of an object formed from an electrically conductive material (e.g., a metal). Alternately, the electrically conductive surface may be a layer of an electrically conductive material (e.g., a metal) formed on an object, wherein the object is formed from an electrically insulating material (e.g., plastic, wood, etc.).
In one embodiment of the method, a positive electrical charge is created on the electrically conductive surface with respect to a reference voltage level. An electron beam is formed, wherein the electron beam includes electrons each having a negative electrical charge with respect to the reference voltage level. The electron beam is directed at the particle. When struck by the electron beam, the particle absorbs a portion of the electrons of the electron beam and acquires a negative electrical charge with respect to the reference voltage level. A force created between the opposed electrical charges of the particle and the electrically conductive surface causes the particle to move from the surface of the semiconductor wafer and toward the electrically conductive surface.
An apparatus is described which embodies the above method. In general, the apparatus includes an electrically conductive surface, a charged particle gun (e.g., an electron gun), and a voltage source. The charged particle gun produces a charged particle beam when activated, wherein the charged particle beam includes particles having a first electrical charge with respect to a reference voltage level. The voltage source is coupled between the electrically conductive surface and the reference voltage level, and creates a second electrical charge on the electrically conductive surface when activated, wherein the second electrical charge is opposite the first electrical charge.
During use, the electrically conductive surface is positioned near the particle to be removed, the voltage source is activated, the charged particle gun is activated, and the charged particle beam is directed at the particle to be removed. When struck by the charged particle beam, the particle to be removed absorbs a portion of the charged particles of the charged particle beam and acquires the first electrical charge, and wherein a force created between the opposed electrical charges of the particle to be removed and the electrically conductive surface causes the particle to be removed to move from the surface of the semiconductor wafer and toward the electrically conductive surface.